Biomechanics

Marathon Stride Rate Dynamics: A Case Study

The purpose of this study was to investigate stride rate (SR) dynamics of a recreational runner participating in his debut marathon. Tibial accelerometry data obtained during a half marathon (R1) and marathon (R2) were utilised. SR data were extracted utilising novel computational methods and descriptive statistics were utilised for analysis of R2, and comparison of the first half of the marathon (R2half) to R1. Results indicate that the participant employed comparable SR strategy in R1 and R2half. For R2 a combined decreasing trend in SR and increased variance in SR from 30 km (R2 =0.0238) was observed. Results indicate that the participant had the ability to maintain SR strategy for the first half of the marathon, however as fatigue onset occurred this ability decreased. Running strategies on SR during fatigue may be of future use to recreational runners.
Listed In: Biomechanics, Gait, Sports Science


Postural Responses to Noisy Support Surface Translations in Stroke Survivors

Healthy standing posture is characterized by the ability to interact with a changing environment while maintaining upright stance. Being adaptable to changing environments affords flexibility and allows the system to encounter novel environments without losing control of posture. The purpose of this research was to determine if stroke survivors could adapt to support surface translations with differing temporal structures. Methods: Eight stroke survivors participated in this research. Participants stood on a force platform on the Neurocom Balance Manager (Neurocom Intl., Clackamas, OR, USA). The support surface was translated in the anteroposterior direction according to waveforms with different temporal structures, this included white noise, pink noise, brown noise, and a sine wave. They also performed a normal standing trial where the platform did not move. Root mean square and detrended fluctuation analysis of the center of pressure signal were calculated to determine amount and temporal structure of variability respectively. Results: During normal standing the stroke survivors’ posture exhibited lack of adaptability. The stroke survivors had increased amount of variability in all conditions compared to normal standing, regardless of the inherent structure of the support surface translations. The temporal structure of variability indicated weakened long-range correlations in all conditions compared to normal standing. This indicates that regardless of the temporal structure of the support surface movement the amount of movement increased while the structure of movement became more random. Previous work has demonstrated that healthy posture is able to adapt to the temporal structure of support surface translations, this adaptability was not seen in a population of stroke survivors. This lack of adaptability makes interactions with environmental perturbations difficult and impacts functionality. Focusing rehabilitation protocols towards regaining healthy temporal structures in postural control could improve functionality in chronic stroke survivors.
Listed In: Biomechanics, Posturography


Fatigue and Recovery in the Shoulder Complex While Performing Simulated Repetitive Work

The shoulder complex affords multiple opportunities for kinematic and muscular variability during repetitive work, which could change physical exposure and risk at work. The purpose of this study was to examine kinematic and muscular adaptations during continued performance of submaximal, repetitive work following a fatiguing protocol. Participants (n=12) completed a sequence of three protocols: (1) 20 pre-fatigue work cycles, (2) anterior deltoid fatigue protocol, (3) 60 post-fatigue work cycles. Each work cycle was 60 seconds and consisted of 4 tasks. Reaction forces and moments were recorded with a 6DOF force sensor (MC3-500, AMTI, Watertown, MA, USA) during the work tasks. The fatigue protocol consisted of static and dynamic efforts targeting the anterior deltoid. Fatigue was quantified through changes in strength, RPE and EMG frequency and amplitude. Activity of 14 muscles of the upper extremity and torso were measured with surface electrodes and kinematics were tracked with a passive motion capture system, 30 reflective markers and a scapular tracker. Immediately following the fatigue protocol, there were significant signs of muscle fatigue and reduced physical capacity. These changes were accompanied by significant muscular and kinematic adaptations in the work tasks during the post-fatigue work cycles (p<.05). Although these adaptations allowed for recovery in some muscles, fatigue persisted and developed in other muscles by the end of the post-fatigue work cycles, despite subjective ratings of perceived exertions returning to pre-fatigue levels. If people are unable to perceive negative behavioral changes during repetitive work, they may be at greater risk of developing workplace injuries.
Listed In: Biomechanics


Hamstring Stiffness is Related to Anterior Tibial Translation when Transitioning from Non-weight Bearing to Weight Bearing

Anterior tibial translation (ATT) is shown to load the anterior cruciate ligament (ACL) as the knee transitions from non-weight bearing (NWB) to weight bearing (WB). Therefore, any factors able to effectively reduce ATT during initial WB would theoretically reduce ACL loading. This study evaluated the extent to which hamstring musculo-articular stiffness (KHAM) is associated with ATT as the knee transitions from NWB to WB in 10 healthy females (19.9 ± 1.5 yrs, 1.65 ± 0.06 m, 62.3 ± 6.3 kg). Linear regression revealed that KHAM predicted 48.6% of the variance in ATT (R^2 = .486, p = .025), with higher KHAM being associated with less ATT. KHAM is modifiable through training, and thus may be an important factor to consider from ACL injury prevention and rehabilitation perspectives.
Listed In: Biomechanics, Sports Science


Muscle force prediction of the lower limb compared to surface EMG at different walking speeds in individual healthy subjects.

BACKROUND: Recent developments in modelling have made it easier to use muscle force predictions to augment clinical gait analysis and enhance clinical decision making. OpenSim claims to provide a straight forward, standardised pipeline (SimTrack) to predict muscle forces implemented in routine processing. This project aims to test SimTrack’s potential in the context of clinical gait analysis by developing a standardised protocol which compares predicted muscle forces with surface EMG at a range of walking speeds. METHODS: 10 healthy participants walked at 3 different speeds (comfortable, ±20%). Kinematics, kinetics and surface EMG of the lower limb were captured. Joint angles and ground reaction forces serve as inputs to predict muscle forces using computed muscle control (CMC) within SimTrack. Predicted muscle forces were compared with EMG to validate the model outputs. RESULTS: Agreement between force prediction and EMG varies between muscles. Some muscles show a general agreement and similar variation with walking speed, others show large unexpected differences between CMC outputs and observed EMG. DISCUSSION: These results suggest that this protocol is running in general. For most walking speeds, CMC muscle forces can be predicted within a timeframe appropriate for clinical purposes. However using the default settings, the model predictions do not agree with EMG measurements. Furthermore, during pilot testing of quicker walking speeds (up to +40%) CMC crashed due the chosen musculoskeletal model being too weak. These findings suggest the need of either different generic parameters or subject specific parameters to obtain valid results. Work is continuing to identify these.
Listed In: Biomechanics, Gait, Other


The Effects of Knee Taping Techniques on Lower Extremity Kinematics During Running

Introduction: Running is a popular form of physical activity linked to various lower extremity injuries. A commonly used technique for injury prevention and rehabilitation is taping. There is considerable research investigating running biomechanics, however, there has been limited to no research examining the effects of gender, speed, and the type of tape used on two-dimensional lower extremity kinematics. Therefore, the purpose of this pilot study was to investigate the effects of gender, speed, and tape on two-dimensional lower extremity kinematics and stride characteristics during running. Method: Eight healthy runners participated (4 males, 4 females). Taping interventions (Leukotape, Kinesio Tape, no tape) and speeds (2.35 m/s, 3.35 m/s) were randomized and lower extremity stride kinematics were obtained using the Peak Motus System at initial contact, midstance, and toe off of running. Comparisons were made using descriptive statistics. Results: Females exhibited greater hip (FIC= 164.04+1.99°; MIC= 167.54+2.12°) and knee flexion (FIC= 167.73+0.93°; MIC= 170.42+1.65°; FPK= 142.83+1.28°; MPK= 146.35+1.21°), while males had greater ankle dorsiflexion (FIC= 88.60+1.00°; MIC= 84.14+1.08°) and plantarflexion (FTO= 51.90+1.01°; MTO= 55.99+0.825°). Females spent more time in support (FCT= 0.28+0.03s; MCT= 0.26+0.02s) while males spent more time in the air (FFT= 0.45+0.02s; MFT= 0.48+0.01s). Faster speed was associated with greater hip flexion and extension (SIC= 167.57+1.95°; FIC= 164.01+2.11°; STO= 197.14+1.23°; FTO= 201.28+0.74°), peak knee flexion (SPK= 145.39+1.82°; FPK= 143.79+2.39°), and less time during contact (SIC = 0.30+0.01s; FIC= 0.25+0.00s). Conclusion: Gender and speed seem to have effects on lower extremity stride kinematics, whereas type of tape does not.
Listed In: Biomechanics, Gait, Other


Effect of Transcutaneous Electrical Nerve Stimulation on Gait Kinematics in Subjects with Anterior Knee Pain

Knee pain is 1 of 5 leading causes of disability by altering lower-extremity muscle function and gait mechanics. While transcutaneous electrical nerve stimulation (TENS) mitigates deficits of muscle function due to pain, it is unclear whether TENS improves gait mechanics. Each of 15 participant (24±3yrs, 71±12kg, 178±7cm) was assigned to the TENS or matched placebo group (23±2yrs, 72±14kg, 177±9cm). Participants underwent 3 different experimental saline infusion sessions (hypertonic, isotonic, control) in a counterbalanced order, separated by 48-h. Hypertonic (5% NaCl) or isotonic (0.9% NaCl) saline was infused into the infrapatellar fat pad for 50-min. No infusion was administered to the control session. Participants and investigators were blinded to the saline solution. A 20-min TENS or placebo treatment was administered, which was blinded to participants. Gait kinematic data were collected using the high-speed video (240 Hz) and force-sending tandem treadmill (1200 Hz) at each time interval (baseline, infusion, treatment, post-treatment). Functional ANOVA (α=0.05) were used to evaluate difference between 2 groups (TENS, placebo) over time. Pairwise comparison functions with 95% confidence interval were plotted to determine specific difference. Hypertonic saline infusion (pain) resulted in increased (1) ankle dorsiflexion (38-75% of stance), (2) knee valgus (20-40%), (3) knee flexion (40-90%), (4) hip adduction (72-100%), (5) hip flexion (50-90%). However, there was no group x time interaction for all kinematics. Altered gait strategies due to pain may play a role in long-term compensation that could have consequences for the joint. TENS treatment, however, did not acutely reduce the deficits in aforementioned kinematic variables.


Listed In: Biomechanics, Gait, Neuroscience, Physical Therapy


Effects of a leaf spring structured midsole shoe on the foot kinematics in overground and treadmill running

The concept of a leaf spring structured midsole shoe (LEAF) is based on shifting the foot anteriorly during the first part of stance phase in heel-toe running. The aim of the current study is to analyze the effects of a LEAF compared to a standard foam midsole shoe (FOAM) on the foot kinematics in overground and treadmill running at two running speeds. Nine male heel strikers ran on a treadmill with the LEAF and the FOAM at 3 and 4 m/s, each for 5 min. Furthermore, the participants performed with both shoes six runs each on a 40 m indoor track at running speeds of 3 and 4 m/s. For one stance phase the ground reaction forces were measured using a force plate imbedded in the track. Running speed and shoe order were randomized. Kinematics (VICON, 200Hz) and kinetics (AMTI, 1000Hz; only overground) were used to calculate the anterior shift of the foot, the foot ground angle at heel strike (FGA at HS) and the horizontal path of the center of pressure (COP). The LEAF increases the anterior foot shift in treadmill and overground running at both running speeds compared to the FOAM, without changing the individuals’ strike pattern. Furthermore, the anterior foot shift affects the COP leading to an overall enlarged COP path. These findings indicate a benefit of the structured midsole on performance at least at moderate running speeds
Listed In: Biomechanics, Sports Science


Joint loading during graded walking with different prostheses - a case study

For lower limb amputees graded walking imposes a high level of motor ability, due to the missing proprioceptive feedback of the limb, and the necessary compensation mechanisms. In order to facilitate gait a focus in prosthesis research is the development of the prostheses ankle joints from rigid to moveable. Therefore, the aim of this case study was to analyse the effects of three different prostheses with a rigid and a moveable ankle joint during graded walking of a unilateral amputee. One male unilateral transfemoral amputee was recruited for this study and a comparison of following three prostheses (endolite, Germany) was performed: Elan (movable ankle joint with flexible resistance), Echelon (movable ankle joint with steady resistance) and Esprit (rigid ankle joint). Kinematic (12 cameras, Vicon, UK, 250 Hz) and kinetic (2 force plates, AMTI, MA, 1000 Hz) data were recorded during self-paced walking on a 6 m ramp, which was set to the inclinations of -12°, -4°, 0°, 4° and 12°. Following gait parameters, ground reaction forces, joint angles and joint moments were calculated. Gait parameters, ground reaction forces and joint angles were marginally influenced by the different prosthetic designs, but major changes occurred on the joint moment level. The use of the rigid ankle prosthesis Esprit induced up to 10 times higher joint moments compared to the moveable ankle joint prostheses. This case study showed that a moveable ankle joint can reduce the joint moments during graded walking, which might be advantageous to use for transfemoral amputees in graded walking.
Listed In: Biomechanics, Gait


Influence of femur rotation and knee valgus on patellofemoral stress

Background: Patellofemoral pain (PFP) is a common condition seen in orthopedic practice. A commonly cited hypothesis as to the cause of PFP is increased patellofemoral joint (PFJ) stress secondary to abnormal lower extremity kinematics (ie. excessive hip internal rotation and knee valgus). However, the influence of these motions on PFJ contact mechanics is unknown. Purpose: To assess the influence of hip rotation and knee valgus on PFJ stress using finite element (FE) analysis. Methods: Patella cartilage stress profiles for a healthy participant were quantified utilizing a subject-specific FE model. Input parameters included: joint geometry, quadriceps muscle forces, and weight-bearing PFJ kinematics. Using a nonlinear FE solver, quasi-static loading simulations were performed to quantify patella cartilage stress during a static squatting maneuver (45° knee flexion). To simulate hip rotation (0-8°) and knee valgus (0-12°), the femur and tibia were rotated in the transverse and frontal plane respectively in 2° increments. Results: Increasing hip rotation resulted in a linear increase in patella cartilage stress. In contrast, increasing knee valgus resulted in a decrease in patella cartilage stress. The combination of hip rotation and knee valgus did not result in higher PFJ cartilage stress compared to isolated hip rotation. Conclusions: Patella cartilage stress appears to be influenced to a greater degree by hip internal rotation as opposed to knee valgus. Surprisingly, higher degrees of knee valgus resulted in decreased cartilage stress (in the absence of hip rotation). Our finding supports the premise that persons exhibiting excessive hip internal rotation may be pre-disposed to elevated patella cartilage stress.
Listed In: Biomechanics, Gait, Physical Therapy